Polystyrene resins are well known in the art and are widely used in industry and in consumer products. Polystyrene resin may be used alone or in polymer blends with other thermoplastic polymers to provide the blends with various advantageous properties. Polystyrene resin is advantageous in that it is inert to many chemical compounds and is generally easy to process, particularly under injection molding techniques. Generally, the physical properties of a specific polystyrene polymer are dependent on the method by which the polystyrene polymer is formed.
For example, the Wright U.S. Pat. No. 3,259,595 discloses polystyrene compositions which are formed by suspension polymerization techniques and which are particularly suitable for expanding to produce a plastic film having a closed cellular structure. Similarly, the Ingram et al U.S. Pat. No. 4,029,869 discloses a method for preparing polystyrene by peroxide-initiated suspension polymerization to provide a polymer product having a broader molecular weight distribution. The suspension polymerization is carried out in the presence of a small amount of a modifying comonomer. The Mace et al U.S. Pat. No. 3,817,965 also discloses the aqueous suspension polymerization of vinyl compounds such as styrene. Mace et al disclose that by carefully controlling the polymerization temperature, high molecular weight polymers exhibiting viscosities of about 9 to about 50 centistokes may be produced.
Additionally, the Pilato et al U.S. Pat. No. 3,645,959 discloses the preparation of high molecular weight vinyl polymers such as polystyrene in non-aqueous dispersions using up to about 1 percent of a diene compound such as norbornadiene. The Gunsher et al U.S. Pat. No. 4,112,209 discloses processes for making polystyrene having a weight average molecular weight Mw between about 200 and about 50,000 and a Mw/Mn ratio of less than about 8 by cationically polymerizing styrene monomer under substantially isothermal conditions in an organic solvent. Highly crystalline isotactic polystyrene polymers having molecular weights less than 1 million may be prepared by the thermal degradation in air of high molecular weight, highly crystalline copolymers of styrene with an alpa-olefin as disclosed in the Hulse et al U.S. Pat. No. 3,700, 639. The Natta et al U.S. Pat. No. 3,435,018 also disclose the production of isotactic polymers of styrene. Specifically, Natta et al disclose the polyermization of monomeric styrene in a heptane solution containing triethyl aluminum catalyst.
As evidenced by the preceding discussion, various methods are known for producing polystyrene resins exhibiting specific physical properties. As the uses for polystyrene resins expand into new fields, it is similarly necessary to develop new methods for producing polystyrene resins exhibiting physical properties required in the new fields of application.